To provide long lives to tools for cutting works at a high feed or speed, dies used under severe molding conditions, etc., it is desired to form hard coatings having excellent oxidation resistance and wear resistance, and various proposals have been made. For example, JP 3877124 B discloses a hard AlTiCrNO coating having a laminate structure comprising a layer A comprising at least Al, Ti, Cr, N and O, the non-metal component being NwO100-w, wherein w is 70-99 atomic %, and having an oxygen content of 1-10 atomic %, and a layer B having an oxygen content of more than 10 atomic % and 30 atomic % or less. JP 3877124 B describes that the oxygen content in the AlTiCrNO coating is controlled by using a mixed gas of nitrogen and oxygen, with their mixing ratio adjusted. However, because the hard AlTiCrNO coating of JP 3877124 B does not have W—O bonds, it fails to satisfy the severe needs of recent higher performance for cutting tools, etc. In addition, because the method of JP 3877124 B uses an oxygen-containing atmosphere, even though a hard coating containing W in place of Cr were formed, oxygen in the atmosphere would predominantly react with Al to form Al oxide, and also react with Ti to form Ti oxide, resulting in an AlTiWNO coating having insufficient oxidation resistance and wear resistance.
JP 4846519 B discloses a target comprising Al, a component M (one or more elements selected from metals of Groups 4a, 5a and 6a, Si, B and S), and Al nitride, the amount of Al nitride contained being 5-30% by mol. JP 5487182 B discloses a target for sputtering, which is made of a Ti—Al alloy containing 1-30 atomic % of Al, Al forming a solid solution with Ti or an intermetallic compound with Ti, and an average oxygen content in the Ti—Al alloy being 1070 ppmw or less. However, because the targets described in JP 4846519 B and JP 5487182 B do not contain oxygen in an amount exceeding an inevitable impurity level, oxygen is introduced into the coating from the oxygen-containing atmosphere. Accordingly, oxygen-containing hard coatings obtained by using the targets of JP 4846519 B and JP 5487182 B do not have sufficient oxidation resistance and wear resistance, like the hard coating of JP 3877124 B.
JP 2009-220260 A discloses a coated tool obtained by forming a W-modified phase having a bcc structure and then a carbide phase on a WC-based cemented carbide substrate, and a hard nitride coating thereon. JP 2009-220260 A describes that the W-modified phase is formed by ion bombardment in an apparatus comprising an arc discharge evaporation source. Specifically, negative bias voltage P1 of −1000 V to −600 V is applied to a substrate at a surface temperature of 800-860° C., and the substrate is irradiated with metal ions (Ti ions) evaporated from the arc discharge evaporation source using a hydrogen-containing Ar gas of 0.01-2 Pa. However, because the hard nitride coating obtained by JP 2009-220260 A does not contain oxygen in an amount exceeding an inevitable impurity level, the resultant coating does not have targeted oxidation resistance and wear resistance. Of course, three targets C1 (for example, Ti100), C2 (for example, Al70Cr30) and C3 (for example, Ti75Si25) used for producing the hard nitride coating of JP 2009-220260 A do not contain oxygen in an amount exceeding an inevitable impurity level.
JP 2008-533310 A discloses a method for forming a hard coating of (AlxCr1-x)yOz in an oxygen-containing atmosphere, using an arc vapor deposition apparatus comprising a target electrode connected to a pulse power source. In the method of JP 2008-533310 A, however, oxygen is introduced from an atmosphere gas without using a target containing oxygen in an amount exceeding an inevitable impurity level, so that the resultant hard coating does not have targeted oxidation resistance and wear resistance.